Ancestral Nikkors with single coatings and no auto indexing. The letters in the lens designations stand for the number of elements, e.g. H=6, O=8, etc.
These lenses will not mount on most modern bodies, film or digital. The D40 is one of the exceptions. No automation. It's like shooting with a Leica M3 which is part of the fun.

I really like them. They look nice, feel nice, and they take a great snap. Artistically, they give away nothing to any modern lens IMHO.